The fuel efficiency of an internal combustion engine is greatest when it is warm, that is, when its oil and coolant have reached their normal operating temperatures. Before these conditions are reached the engine operates at sub-optimal efficiency. Consequently, measures to expedite the warm-up, particularly of engine oil, but also of coolant, will decrease a vehicle's fuel consumption.
It is further known that the production of exhaust emissions from an engine are high when the engine is first started from cold. That is to say, when the engine is cold more emissions are produced for a specific fuel consumption compared to the situation when the engine is operating at, or substantially at, its normal running temperature.
It is desirable to reduce the fuel consumption of an engine in order to reduce the running costs of the engine and the emissions from the engine. It will be appreciated by those skilled in the art that the emissions from an engine are closely related to the volume of fuel consumed by the engine and this is particularly so in the case of CO2 emissions.
Two factors of an engine cold start affecting fuel economy are:
1) Cold Start Cranking (CSC); and
2) Engine Warm Up (EWU).
For CSC the starter motor normally rotates an engine with cold, thick, viscous engine oil and poor lubrication, and hence high friction internal engine components. Both high oil viscosity and poor lubrication increase demand for the starter motor, directly putting an additional drain upon the vehicles battery. The battery charge is replenished via the alternator, when the engine has started, but at a cost to fuel economy.
For EWU, once the engine has started, the engine again works harder to overcome the cold and viscous engine oil until optimum engine operating temperatures and related low oil viscosity is achieved. During EWU extra fuel is consumed to compensate for higher frictional losses at a further cost to fuel economy.
It is therefore known that reducing the viscosity of a conventional lubricant used to lubricate an engine is desirable in general, but specifically during the warm up phase. Decreasing lubricant viscosity reduces fuel consumption due to reduced frictional losses, reduced pumping losses and a reduction in the power required to pump the lubricant through the engine.
Many modern engines have variable oil pumps for engine lubrication. These vary the flow rate of lubricant passing through the engine with the intention of minimizing the parasitic losses of the oil pump and thereby increasing fuel efficiency. For instance, at low load operating points the oil pump is set to provide a low flow rate output. Conversely, at high load operating conditions such as at peak power, the oil pump is set to provide close to maximum flow rate output. In other words, the flow rate is matched to the demand of the engine. An undesired implication of this matching is that the oil will not warm-up as quickly thereby having a detrimental effect on fuel consumption and emission production. It will also be appreciated that improving the warm-up rate of the coolant circulating through an engine is beneficial because this will also have an effect on fuel efficiency and emission production. It is an object of this disclosure to provide a method of improving engine warm-up in a fuel efficient manner.
To solve at least some of the aforementioned disadvantages a method to increase the rate of engine warm-up is provided. The method comprises opening a flow control valve in a liquid circuit when the temperature of the liquid within the liquid circuit is above a predefined threshold temperature. Then constricting the flow of the liquid within the liquid circuit when a temperature of the liquid is below the predefined threshold temperature and a vehicle deceleration rate is above a predefined deceleration rate. In addition to confining the restriction of liquid flow to a period when the vehicle is decelerating, the method could be enacted when the vehicle is in an over-run situation, but not necessarily decelerating, or when prevention of acceleration is advantageous, such as maintaining speed during a downhill descent. This constriction of a line within the liquid circuit requires more work of a pump within the liquid circuit. The inefficient operation of the pump creates heat transferable to the liquid, more readily warming it up and decreasing liquid viscosity. Enacting the method of the present disclosure when the vehicle is decelerating minimizes, or negates, negative impact of inefficient pump operation on fuel economy and overall engine efficiency.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.